AbstractFloristic investigations in the western Eurasian area of Fagus L. were carried out to provide a basis for comparison with European Late Tertiary plant assemblages containing Fagus. Beech turned out to be part of polydominant forests in marginal regions of its range. It is of interest that Fagus occurs together with a number of evergreen species not only in the well known Tertiary relict areas of Northern Turkey and western Georgia, but also in Southwestern Europe. Coastal stands in the Georgian Colchic area with high atmospheric humidity turned but to be most significant for the actualistic approach. Small‐scale mosaic patterns of distinct vegetation units could be observed. They are caused by differences in soil drainage and fluctuating ground water levels. Such conditions are supposed to be very similar to Neogene vegetation types reflected in the fossil record.Spontaneous spreading of exotic plants in Georgian mixed broadleaved evergreen forests but also in southern Switzerland demonstrates the abundance of free niches in contemporaneous broadleaved forests. Climates with evenly distributed high amounts of annual precipitation and no severe winter and late frosts seem to favour such phenomena.Monodominant beech forests are derived vegetation types of the postglacial period and occur throughout the whole area of Fagus in western Eurasia.